1. Field of the Invention
The present invention relates to short range communication systems, apparatus and methods using the human body and air as a medium, for example for medical devices and partially implantable medical systems.
2. Related Art
In many applications, it is necessary for devices located near, on, or within the human body to communicate with each other. For example, a partially implantable device may need to transmit and receive data from another externally located device near or on the body, or several devices may need to exchange information. Wired communications are reliable, but may not be aesthetically pleasing, or practical.
Conventional near field, radio frequency communications experience various practical issues in such applications. Conventional RF communications in particular experience relatively large power losses when transmitting across the body.
One proposal to address this is the use of electrostatic fields. Such arrangements are disclosed in T. G. Zimmerman, “Personal Area Networks: Near-field intra-body communication” (IBM Systems Journal, vol. 35, No. 3&4, 1986, pp. 609-617), and in U.S. Pat. No. 5,914,701. Zimmerman's method makes use of two electrodes per device, and forms two separate signal routes between the human body and an earth ground. This creates issues if the earth ground and human body ground are brought in to contact.
U.S. Pat. No. 6,223,018 to Fukumoto discloses a communication device using a time varying electric or electrostatic field with a carrier frequency from several tens of KHz to several MHz.
Other short range wireless communication methods and systems are based upon generating and capturing the potential difference signal in a frequency band such that a quasi-electrostatic field formed within the human body is dominant over a radiation field formed outside the human body when the transmitting electrode and the receiving electrode are each disposed in very close vicinity to the human body. For example, U.S. Pat. No. 7,181,024 to Oba et al discloses an arrangement for use with a personal audio apparatus. Body contact electrodes are associated with the headphones and the playback apparatus. The audio signal is modulated onto a carrier frequency of 2 to 30 MHz. U.S. Pat. No. 6,118,882 to Haynes discloses the use of radio frequency signals transmitted through the human body to communicate between a base device and earphones, wherein each earpiece advantageously includes a coil.